Generate tear-off closures dynamically.

dart/tests/compiler/dart2js_extra/mirror_invalid_invoke2_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Test that we cannot reflect on elements not covered by the `MirrorsUsed`
 // annotation.
 
 library test;
 
 @MirrorsUsed(targets: 'C.foo')
@@ skipping 11 matching lines @@
   bar() => () => 2;
 }
 
 main() {
   var c = new C();
   c.bar();  // Call bar, so it is included in the program.
 
   var mirror = reflect(c);
   Expect.equals(1, mirror.invoke(const Symbol('foo'), []).reflectee);
   Expect.throws(() => mirror.invoke(const Symbol('bar'),  []),
-                (e) => e is UnsupportedError);
+                (e) => e is NoSuchMethodError);
 }